


Like Brother, Like Sister

by Hidden_Joy



Category: Mortal Instruments Series - Cassandra Clare, Shadowhunter Chronicles - Cassandra Clare, Shadowhunters (TV)
Genre: Don't Hurt My Brother, Don't Hurt My Sister, F/M, Fluff, Humor, M/M, Magnus is Scared of Isabelle, Relaptionship Fluff, Sibling/Sibling's Lover Talk, Simon is Terrified of Alec, This is serious hilarious, fashion advice, siblings fluff
Language: English
Status: Completed
Published: 2016-05-28
Updated: 2016-05-28
Packaged: 2018-06-08 06:51:36
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,033
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6843733
Author URL: https://archiveofourown.org/users/Hidden_Joy/pseuds/Hidden_Joy
Summary: <blockquote class="userstuff">
              <p>Alec and Izzy turn out to be more alike than they care to admit.</p><p>Or</p><p>Alec and Izzy both decide to warn their sibling's boyfriend not to hurt the other.</p>
            </blockquote>





	Like Brother, Like Sister

"Magnus! I'm glad you're here!" Izzy said hurriedly, her heels clanking loudy against the Institute floor as she speed-walked toward her brother and his boyfriend.

The two looked at her with furrowed eyebrows as she grabbed Magnus' arm, standing beside him.

"Don't you have that date with Simon tonight? Shouldn't you be getting ready?" Alec asked, raising an eyebrow at his sister.

"Yes, I do, and that's why I need Magnus!" she explained, flashing the warlock a red-lipped smile. The warlock smiled elegantly at her as she spoke next, looking at her brother. "I need him to help me pick out what to wear. I have absolutely no idea and Alec, you've been blessed with a boyfriend with impeccable fashion sense," Izzy gushed.

Magnus grinned at her, while Alec blushed a bit, but smiled at the word 'boyfriend', as he did every time. 

"Oh, I'm more than willing to help, dear. Alexander, if you will excuse us," Magnus spoke, then to his boyfriend, his chin raised. 

"By all means, go ahead," Alec laughed, waving them off.

"Oh! If Simon gets here, just let him in and tell him I'm still getting ready. Thanks, big brother," Izzy instructed, then dragged the warlock off with her. 

Alec rolled his eyes a bit, but smiled. Oh, he'd let Simon in, all right. 

As if on cue, the Institute's doorbell sounded. Alec strode down the steps and down the entrance hall. He pulled open the door and Simon stood on the other side, standing straight.

He was dressed in a mix between casual and formal, wearing a button up and skinny jeans. Alec surveyed him a moment with a raised eyebrow before stepping aside with a breath and letting the vampire in.

Simon smiled, stepping inside beside Alec. "Uh, where's-"

"Upstairs getting ready," Alec cut him off, shutting the door behind Simon and crossing his arms over his chest and facing him.

"Ah," Simon mumbled, his eyes shifting down the hall.

"Yeah, Magnus is helping her pick out an outfit," Alec added, laughing a bit. Mind as well start nice. Simon laughed as well.

"Well, she'll look beautiful in anything," Simon stated simply. Alec smirked a bit.

"Yeah, she will," he agreed. "And you better keep thinking that," Alec told him, his voice turning serious as well as his expression. Alec straightened a bit, making himself look more intimidating.

"Um, wh-what?" Simon asked, his eyes widening a bit as he looked at Alec in confusion.

"I just mean that Izzy is my little sister and I love her to pieces," he explained, taking a step closer so he was looking down at the vampire. "And if _anyone_ were to hurt her, they would be torn to shreds. But, I trust you not to. Right, vampire?" Alec asked, flashing Simon a stiff smile.

Simon's eyes were wide and Alec could see nervousness clear on the vampire's face. "I-I would never want to hurt Izzy," Simon explained.

Alec smiled a friendly smile then. "Good. Let's keep it that way, huh?" he said with his eyebrows raised and patting Simon's arm.

Simon nodded frantically. Alec was sure if Simon's heart could beat, it would be pounding. He smirked then, stepping back with a curt nod as he heard heels clanking on the stairs.

[][][][][][][]

"You know, Izzy, I think something red would really compliment your sk-"

"I already know what I'm wearing," Izzy cut the warlock off as she shut the door to her bedroom firmly. Her expression was now serious, her arms crossed over her chest as she stared at Magnus.

Magnus frowned, blinking at her a moment before speaking. "Izzy, dear, what's wrong? Why did you need me then?" he asked, concerned for the younger Lightwood.

"We need to talk," she stated simply. She walked passed Magnus, then, grabbing the red dress on her bed and starting to change. Magnus wasn't very surprised by Izzy's boldness and confidence, but her tone made him a bit bewildered.

"Well, what is it?" he asked as she slipped the dress on.

"You," she started, straighting and pulling her hair from the collar, "are dating my brother," she stated simply.

"Is that a problem? I thought you were happy for us?" he asked, a bit hurt by what he thought this could be about.

"I am!" she assured quickly. "Alec is the happiest he's ever been, and that's all I've ever wanted. But," she spoke, "I don't want you hurting him," she explained.

Magnus looked at her, offended. "I would  _never_ hurt Alexander," Magnus promised, shaking his head.

"I believe you," she promised back. Her next sentence was spoken much less kindly. "I just want you to know, that if there ever comes a day where you hurt him accidently, or no longer feel that passionatley about not hurting him," she spoke, her voice growning sharp and she stepped close, a perfectly painted nail coming up and pointing at the warlock. "I will take my whip and make sure you can never walk again, Magnus Bane," she told him, her eyes narrowed.

The warlock's eyes flew wide. He was clearly scared now. "I promise you that will never happen," he spoke, his words still spoken with confidence.

"Good," she answered, then stepped back. "Come on, Simon's probably here already."

Magnus nodded and followed the female Lightwood out of the room and back down to the main floor. 

They found Simon and Alec near the entrance, Simon looking slightly nervous and Alec looking proud of himself.

Simon looked relieved as the two aproached. "Ready?" he asked Izzy.

"Ready!" she answered, smiling. She slid her arm through Simon's, who grinned. "Later, big brother, Magnus!" she told the two, sending a wink the warlock's way as he moved to stand beside Alec, a hand on his arm.

"Bye," Simon waved at the two, but not looking directly at Alec. The two left then and Alec started laughing.

"What, what's so funny?" Magnus asked, laughing at Alec's hysterics.

"Oh, you are gonna love this story," Alec started.

"Well, I have a story for you, actually," Magnus answered.

"Oh, do you?" Alec asked, raising his eyebrows.

"I do," Magnus grinned, then took Alec's hand and led him off. 

**Author's Note:**

> Hope you liked it!
> 
> Follow me on Tumblr at jonnorlandfill.
> 
> I do not own the Shadowhunters show or books or anything you recognize.
> 
> -HJ


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